1. Field of the Invention
This invention relates to a method and a functional material for selective separation of carbon dioxide gas from the effluent gas emanating from energy plants and chemical plants which use fuels having hydrocarbons as main components thereof.
2. Description of the Related Art
This invention further relates to a shaped article obtained by molding the functional material in a prescribed shape and to an apparatus for effecting the selective separation of carbon dioxide gas from the effluent gas emanating from energy plants and chemical plants which use fuels having hydrocarbons as main components thereof by the use of the functional material and/or the shaped article.
In recent years, from the standpoint of conserving the earth's environment, the increase of the concentration of the carbon dioxide gas in the atmosphere has come to pose a problem. For the purpose of decreasing the gross amount of the carbon dioxide gas that is released into the atmosphere, an attempt has been made to harness a gas turbine or a fuel cell for either recovering and recycling the carbon dioxide gas from the effluent gas emanating from energy plants and chemical plants which use fuels having hydrocarbons as main components thereof or depriving the effluent gas of harmfulness.
Ishikawajima-Harima Technical Report, Vol. 34, No. 2, pp. 83-92, for example, discloses a molten carbonate fuel cell system which recovers from the effluent gas of a fuel cell the carbon dioxide gas formed by the electrode reaction and puts the recovered carbon dioxide gas to reuse.
To be specific, in the molten carbonate type fuel cell, the electrode reactions represented by the formulas (10) and (11) in FIG. 6 occur. This molten carbonate fuel cell system is intended to reclaim the carbon dioxide gas by recovering the carbon dioxide gas produced on an anode (fuel electrode) 27 side and then supplying the recovered carbon dioxide gas toward a cathode (air electrode) 28 side as indicated by the arrow marks in FIG. 6.
Incidentally, in the molten carbonate type fuel cell, since the effluent gas is generally a mixed gas containing steam, hydrogen, carbon monoxide, and methane besides carbon dioxide gas, the carbon dioxide gas must be selectively separated from this effluent gas.
Generally, as typical means to implement this selective separation of carbon dioxide gas from the effluent gas of this quality, the absorption liquid method which uses an alkanol amine type solvent and the membrane separation method which utilizes a cellulose acetate membrane have been known to the art.
These methods, however, require to create a difference of pressure between the carbon dioxide gas supply side and the carbon dioxide gas collection side through the medium of a separation membrane. To be specific, they attain the collection of carbon dioxide gas by heightening the partial pressure of carbon dioxide gas on the carbon dioxide gas supply side and lowering the partial pressure of carbon dioxide gas on the carbon dioxide gas collection side and consequently inducing the exclusive passage of the carbon dioxide gas through the separation membrane toward the carbon dioxide gas collection side by virtue of the difference of the partial pressure of the carbon dioxide gas which is attendant on the pressure difference. They consequently demand a contrivance which is capable of controlling the difference of pressure between the carbon dioxide gas supply side and the carbon dioxide gas collection side and, therefore, entail the problem that they cannot be easily utilized generally.
Further, since the solvent and the membrane which are used by these methods are deficient in resistance to heat, they both require the temperature of the effluent gas below about 200.degree. C. In such systems emitting effluent gases at elevated temperatures as are typified by the molten carbonate type fuel cell which emits the effluent gas of about 600.degree. C, therefore, the step for cooling the effluent gas as by means of heat exchange constitutes itself an essential requirement for the separation of the carbon dioxide gas from the effluent gas. Since the separation of the carbon dioxide gas from the effluent gas consumes energy copiously, these methods have the problem that they cannot be easily utilized generally.